Method for treating industrial waste

ABSTRACT

Disclosed herein is a method for removing contaminants from an industrial fluid waste. The method comprises the steps of ozofractionating the industrial fluid waste whereby contaminants are oxidised and a foam fractionate is formed; and separating at least a portion of the foam fractionate and any precipitate from the ozofractionated fluid.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/236,317, filed Jan. 30, 2014, which is a national stage entry ofPCT/AU2012/000924, filed Aug. 3, 2012, which claims priority toAustralian application 2011903114, filed Aug. 3, 2011; and U.S.application Ser. No. 14/236,317, filed Jan. 30, 2014 andPCT/AU2012/000924, filed Aug. 3, 2012, are incorporated herein byreference.

FIELD

The present invention relates to methods for treating industrial fluidwastes.

BACKGROUND

Industrial fluid waste usually requires treatment before it can besafely discharged into the environment. Industrial fluid wastes oftencontain high amounts of contaminants such as organic compounds and heavymetallic species, and these contaminants need to be removed (orsignificantly reduced) before the waste is safe for disposal.

For example, acid mine (or metalliferous) drainage (AMD) is anindustrial fluid waste that causes significant problems in the miningindustry. AMD occurs when sulfide minerals in rocks are exposed tooxidizing conditions, for example, in coal and metal mining, highwayconstruction or other large-scale excavations. There are many types ofsulfide minerals, but iron sulfides (common in coal regions), pyrite andmarcasite (FeS₂) are the predominant AMD producers. Upon exposure towater and oxygen, pyritic minerals oxidize to form acidic, iron andsulfate-rich water.

Existing techniques for treating AMD include exposing the AMD to basicagents such as lime, which raises the pH of the AMD and causes manymetallic species to precipitate. The precipitate is then allowed tosettle and the treated water decanted. Other techniques, such as thatdescribed in U.S. Pat. No. 6,485,696, use ozone to rapidly oxidisespecific metallic elements present in AMD. Ozone is bubbled through theAMD, which oxidises the metallic elements and causes them toprecipitate. This technique may also involve the step of adding a basicagent to the ozone-treated water to cause other metallic elements toprecipitate.

SUMMARY

In a first aspect, the present invention provides a method for removingcontaminants from an industrial fluid waste. The method comprises thesteps of ozofractionating the industrial fluid waste, wherebycontaminants are oxidised and a foam fractionate is formed, andseparating at least a portion of the foam fractionate and anyprecipitate from the ozofractionated fluid.

Ozofractionation is a technique that combines foam fractionation withozone. Foam fractionation can be used to separate certain species from afluid by passing a foam through the fluid. Any air/water interface has asmall electrical charge and, as foam fractionation creates millions oftiny bubbles, an extremely large air/water interface is created. Thecorresponding electrical charge is a powerful attractant to dissolvedorganic molecules, minerals, trace elements and colloidal sizedparticles. As the electrical charge of an ozone/water interface issignificantly greater than that of an air/water interface, the inventorhas found that ozofractionation provides a far more aggressiveseparation and decontamination than traditional foam fractionation.Indeed, the inventor has found that ozofractionation is aggressiveenough to oxidise the majority of contaminants typically found inindustrial fluid waste. The oxidation power of ozofractionation is manytimes greater than that which can be achieved by simply bubbling ozonegas through a solution. Furthermore, many contaminants may notprecipitate upon exposure to ozone simply bubbled through a solution.However, when exposed to ozofractionation, such contaminants may eitherprecipitate or get caught in the rising foam of ozone and become part ofthe foam fractionate, which is readily separable from the hulk fluid.Ozofractionation of industrial fluid waste causes more effectiveprecipitation of contaminants than bubbling ozone through the fluid. Inaddition, during ozofractionation, many other contaminants such ashydrocarbon based compounds (e.g. hydraulic fluids, petroleum basedproducts, etc.) are broken down by the ozone and trapped in the foam.

Ozofractionation has been used for many years in the aquacultureindustry, primarily to remove dissolved organics such as fats and oilsand debris from an aquarium or pond.

The inventor recognised that ozofractionation might also be capable ofdecontaminating industrial fluid wastes, and has spent a number of yearsdeveloping ozofractionation systems capable of processing such wastes.

As used herein, the term “industrial fluid waste” will be understood toinclude fluid wastes produced by industrial processes, including wastesthat are contaminated with environmentally degrading levels of toxicelements, minerals or complex volatile organic compounds. Exemplaryindustrial fluid wastes are organic or inorganic pesticides, fertilisers(nitrogen and phosphorous based) organic pollutants (e.g. volatileorganic compounds—VOCs), oil, grease and other petrochemical compounds,acid mine drainage, acid rock drainage or industrial waste water fromelectrical power plants, steel plants or mines. The term “industrialfluid waste” does not encompass waste produced by domestic processes,such as sewerage, which are generally most effectively treated usingorganic methods.

In a second aspect, the present invention provides a method for removingdissolved metals from mine waste water. The method comprises the stepsof ozofractionating the mine waste water, whereby species containing themetals precipitate, and separating the precipitated metal species fromthe ozofractionated water.

In some embodiments, the method of the second aspect may comprise afurther step in which parameters of the ozofractionated water aremonitored and, if necessary, a reagent to adjust pH is added to theozofractionated water.

In a third aspect, the present invention provides a system for treatingacid mine drainage. The system comprises an ozofractionator adapted toreceive and ozofractionate the acid mine drainage under conditionsdetermined from measured parameters of the acid mine drainage; a storagetank for receiving the ozofractionated acid mine drainage, whereby metalspecies that precipitated during ozofractionation are allowed to settle;and means for removing supernatant ozofractionated acid mine drainagefrom the storage tank and, if measured parameters of the supernatantozofractionated acid mine drainage are within acceptable environmentallimits, discharging the supernatant ozofractionated acid mine drainage.More specific features of the system of the present invention aredescribed below in the context of the methods of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described by way ofexample only with reference to the accompanying drawings in which:

FIG. 1 is a drawing of an ozofractionation chamber for use in anembodiment of the present invention; and

FIG. 2 is a process flow diagram depicting an embodiment of the presentinvention for treating acid mine drainage.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a method for removing contaminants froman industrial fluid waste. The method comprises the steps ofozofractionating the industrial fluid waste, whereby contaminants areoxidised and a foam fractionate is formed, and separating at least aportion of the foam fractionate and any precipitate from theozofractionated fluid.

Ozofractionation combines foam fractionation with the aggressiveoxidising properties of ozone. Ozone is a powerful oxidising agent and,under appropriate conditions, will oxidize most metals (except gold,platinum, and iridium) to oxides of the metals in their highestoxidation state. When the ozone is in the form of a foam comprising tinybubbles comprising ozone, the amount of ozone exposed to the industrialfluid waste is many times greater than that which can be achieved bysimply bubbling ozone through the fluid, and ozofractionation thereforeprovides a much stronger oxidising environment. Thus, exposing anindustrial waste fluid containing metallic species (e.g. inorganiccompounds or minerals) to ozone causes the metals to be oxidised and theoxidised metal species will typically precipitate. The precipitate cansubsequently be either gravity separated, fractionated or mechanicallyfiltered from the fluid.

Ozone will also oxidise most organic compounds (including complexvolatile organic compounds). Thus, exposing an industrial waste fluidcontaining organic compounds to ozone causes the organic compounds to beoxidised and effectively destroyed. Typically, the oxidised remains ofthe organic compounds either precipitate or become associated with thefoam fractionate and hence may be separated from the ozofractionatedfluid. As the bubbles comprising ozone are so small, when they float tothe top of the industrial fluid waste they remain stable and are able tobe separated (along with any contaminants associated with the foam) fromthe ozofractionated fluid.

Ozone is more soluble in water than oxygen and any residual ozonepresent in water decays rapidly. Once ozone enters water, it follows twobasic modes of reaction: direct oxidation, which is rather slow andextremely selective, and auto-decomposition to the hydroxyl radical. Thehydroxyl radical is extremely fast and non-selective in its oxidation oforganic compounds. Hydroxide ions are also formed when the ozone enterswater and will oxidise certain compounds (e.g. some compounds found inpesticides). If the ozone in the water is exposed to UV light, theproportion of hydroxyl radicals will tend to decrease and the proportionof hydroxide ions increase. Thus, in some embodiments and, depending onthe nature of the contaminants in the industrial fluid waste, thebubbles of ozone may be exposed to UV light.

As discussed above, the oxidation power of ozofractionation is manytimes greater than that which can be achieved by simply bubbling ozonegas through a solution, and the inventor has discovered thatozofractionation can be used to decontaminate many industrial fluidwastes. Indeed, for some industrial fluid wastes, substantially all ofthe contaminants may be removed by ozofractionation. In someembodiments, however, additional treatment steps may be required beforethe waste is ready for discharge. Such additional treatment steps willbe described in further detail below.

Any industrial waste that is contaminated with a potentiallyenvironmentally degrading substance can be treated using the methods ofthe present invention. Such degrading substances may vary from specieswith only mild environmental concern to species that, even in extremelylow dose, may cause death or are carcinogenic, teratogenic or mutagenicto aquatic invertebrates and vertebrates. Exemplary contaminants thatcan be removed from industrial fluid waste using the method of thepresent invention include pesticides, organic pollutants, contaminantsassociated with acid mine drainage or acid rock drainage, orcontaminants typically found in industrial waste water from electricalpower plants, steel plants or mines.

In one particular application, the method of the present invention hasbeen used to reduce the amount of the banned pesticide DDT(dichlorodiphenyltrichloroethane) present in industrial waste water. Themethod of the present invention was used to reduce DDT from 108 partsper billion to <2.0 parts per billion in industrial wastewater, and alsoused to reduce the amount of DDE (dichlorodiphenyldichloroethylene,which is a metabolite or breakdown product of DDT) in industrial wastewater from 9.5 parts per billion to <0.5 parts per billion.

In some embodiments, the industrial fluid waste is ozofractionated bycausing a foam comprising ozone to pass through the industrial fluidwaste. Typically, the industrial fluid waste is caused to flow through achamber whilst a foam comprising ozone is caused to rise from a bottomportion of the chamber to a top portion of the chamber.

Depending on the nature of the industrial fluid waste, the foam mayeither comprise ozone and another gas (e.g. air), or consist only ofozone.

In some embodiments, the industrial fluid waste is caused to flowthrough a chamber in an opposite direction to a foam comprising ozonethat is rising from the bottom portion of the chamber to the top portionof the chamber. Such a counter-current flow enables a longer contacttime between the ozone bubbles and the industrial fluid waste becausethe tiny bubbles become entrained in the flow of the waste, therebyspending more time in contact with the waste, thereby providing moreefficient ozofractionation.

The foam comprising ozone may be delivered to the industrial fluid wasteusing any technique capable of dispersing a foam in a fluid, forexample, by venturi injection. Typically, the size of the bubblescomprising ozone delivered into the fluid should be less than or equalto about 200 μm in diameter (e.g. less than or equal to about 150 μm indiameter). The inventor has found that if the bubbles are significantlylarger than this they do not tend to form a stable foam on top of theozofractionated fluid, but can burst and release the trappedcontaminants back into the ozofractionated fluid. Further, the largerthe bubble, the less ozone that is available to oxidise contaminants inthe fluid waste.

In some embodiments, the foam comprising ozone may be exposed to UVlight. If so, the UV exposure is typically performed after the foam hasbeen produced in the venturi, but before the foam contacts theindustrial fluid waste.

In some embodiments, the method comprises a preliminary step in whichparameters of the industrial fluid waste are monitored and used todetermine ozofractionation conditions (e.g. length of time ofozofractionation required or quantity of ozone to be added) required inorder to effectively remove the contaminants in the industrial fluidwaste.

The duration of ozofractionation will depend on the nature of theindustrial fluid waste and can be determined empirically. For heavilycontaminated wastes, ozofractionation times may be from about 1 hour toabout 4 hours (e.g. from about 1 hour to about 3 hours or from about 1hour to about 2 hours or about 1.5 hours). For lightly contaminatedwastes, ozofractionation times may be as little as 30 seconds, but morecommonly will be from about 5 minutes to about 45 minutes (e.g. fromabout 15 minutes to about 35 minutes or from about 20 minutes to about30 minutes or about 25 minutes). In some embodiments, the industrialfluid waste is ozofractionated for about one hour.

The quantity of ozone required to effectively ozofractionate anindustrial waste fluid will also depend on the nature of the industrialfluid waste and can be determined empirically. For heavily contaminatedwastes, about 1 to about 4 grams (e.g. from about 1 g to about 3 g,about 2 g to about 3 g or about 2.5 g) of ozone for every kilolitre ofindustrial fluid waste may be required. For lightly contaminated wastes,about 0.5 to about 1 grams (e.g. from about 0.7 g to about 1 g, about0.7 g to about 0.9 g or about 0.75 g) of ozone for every kilolitre ofindustrial fluid waste may be required. In some embodiments, theindustrial fluid waste is ozofractionated using about 4 grams of ozonefor every kilolitre of industrial fluid waste.

Usually, the source of the industrial fluid waste will be studied toassess the worst case scenario to provide an adequate c.t(concentration×time) of ozone to enable complete oxidisation of allpossible contaminates in the waste. As will be appreciated, c.t can beregulated by changing either the ozone concentration or contact time.For example, delivering 4 g of ozone over 1 hour is equivalent todelivering 1 g of ozone over 4 hours or 20 g of ozone over 12 minutes.Thus, the quantity of ozone and contact time can be varied depending onthe rate at which the industrial fluid waste requires treatment.

Generally, the c.t for treating a given industrial fluid waste would besufficient to treat industrial fluid waste containing at least twice theworst case scenario of contaminants. However, the c.t should alsocontrol the ozonation as a function of energy efficiency by dosing thelowest possible concentration of ozone to achieve the result whilegiving capacity to effectively treat twice the strength envisaged as theworst possible scenario.

Any precipitate that forms during ozofractionation should be separatedfrom the fluid. Any such precipitate may, for example, be separated fromthe ozofractionated industrial fluid waste by allowing the precipitateto settle and decanting the supernatant water. Other methods forseparating the precipitate and fluid, such as filtration, could also beused.

In some embodiments, it may be necessary to further treat theozofractionated fluid before it is safe to discharge into theenvironment. Such further treatment will depend on the nature of theindustrial fluid and its contaminants. Specific further treatments aredescribed below in the context of treating mine waste water, and may beapplicable to other industrial fluid wastes.

An embodiment of a system for ozofractionating an industrial fluid wastewill now be described with reference to FIG. 1.

In the system depicted in FIG. 1, a column of tiny bubbles is caused tomove upwards through a chamber 10 into which a stream 12 of anindustrial fluid waste is continuously introduced via an inlet 14 closeto the top of the chamber 10 and continuously removed (at the same rate)via an outlet 16 close to the bottom of the chamber 10. The chamber 10also includes a zone 18 above the surface of the fluid in the chamberwhere a foam 20 forms and can be removed.

Ozone is generated in an ozone generator 22 and directed into a venturi24, where it is mixed with fluid pumped from the bottom of the chamberby ozofractionation pump 26. The ozone is vigorously mixed with theliquid in the venturi 24 such that a foam comprising tiny bubbles ofozone are produced. The ozone foam is injected into and distributedrelatively evenly across the full cross-sectional area of the chamber 10via distribution pipes 28 (not depicted in the chamber 10 for clarity).

Once the ozone foam has been injected into the chamber 10, it slowlyrises to the surface of the fluid at the top of the chamber 10 and forma foam in the zone 18. As the foam rises, they attract contaminantspresent in the waste stream 12 and the contaminants thereby come intocontact with and are oxidised by the ozone. A majority of the oxidisedcontaminants then either precipitate out of the solution and start tofall to the bottom of the chamber 10 to join sediment pile 30, orassociate with and continue to rise with the ozone foam.

Once the foam bubbles reach the surface of the fluid in the chamber,they float on top of the surface in the zone 18 whilst excess fluiddrips from them back into the main body of fluid in the chamber 10. Asmore foam bubbles reach the surface of the fluid, the lighter foam risesand is directed by foam concentrator 32 into fractionate chamber 34. Thefoam that reaches fractionate chamber 34 is laden with contaminants andcan be disposed of or further processed as necessary.

The precipitate in the sediment pile 30 is periodically pumped out ofthe chamber using sediment pump 36. The precipitate is laden withcontaminants and is disposed of or further processed as necessary.

The fluid removed from the chamber via outlet 16 has been in contactwith the ozone foam for enough time to ensure that a significantproportion of the contaminants in the industrial fluid waste introducedinto the chamber via inlet 14 have been removed (either viaprecipitation or the foam).

Relevant parameters to consider during ozofractionation include:

A: Bubble size—the smaller the bubble the higher the charged surfacearea and the more stable the resultant foam fractionate.

B: Bubble generation method—ideal bubble size is less than or equal toabout 200 μm.

C: Ratio of ozone to fluid in the bubble—usually about 13% (v/v) ozoneto water, but will vary (downwards) dependent on bubble size. Above 13%the bubbles tend to combine, which reduces the effectiveness of theprocess.

D: Bubble distribution method—bubbles should be evenly spread into thechamber with emphasis on creating an evenly distributed rising bubblemass in the chamber. If a single bubble source is inadequate to achievethis result, multiple venturis can be used. For instance, a 1.5 mdiameter chamber will benefit from 6 venturi sources with internalplumbing that spreads the bubble mass out across the chamber.

E: Ratio of height to width of the chamber—it is important avoidconditions where portions of the industrial fluid waste can avoidcontact with the rising bubble mass.

F: Shape of foam chamber and dewatering tower—this is necessary tostabilise the bubble mass such that foam will build up with even thesmallest concentrations of contaminate, and at the same time allowexcess fluid to drain back downwards leaving a foam that removes thecontaminates but not too much fluid. The fractionate collection cupshould also hold a stabilised fractionate, where the bubbles have alldegraded such that the fractionate is free of air and stable forsubsequent removal (e.g. by gravity) to a decant and dewatering process.

G: Flow rate through the chamber—the retention time of the industrialfluid waste in the chamber should be calculated based on the worst casecontamination scenario and the highest flow rate of industrial fluidwaste. In general, a minimum 1 hour retention is required, but this maybe modified (depending on the nature of the contaminants) by increasingor decreasing the amount of ozone injected into the chamber.

In one application, the present invention can be used to removecontaminants from mine waste water (e.g. waste water containing acidmine drainage, acid rock drainage, process water from mill operations ormining vehicle wash down water). The present invention therefore alsoprovides a method for removing dissolved metals from mine waste water.The method comprises the steps of ozofractionating the mine waste water,whereby species containing the metals precipitate, and separating theprecipitated metal species from the ozofractionated water.

When waste water from mining operations is ozofractionated, the majorityof metallic species present in the water (including species containingmetals selected from the following: iron, manganese, silver, nickel,cobalt, bismuth, palladium, thallium, aluminium, zinc, copper, lead,arsenic and chromium, as well as other typical mining based contaminantssuch as cyanide) are oxidised and subsequently precipitate.Ozofractionation also typically increases the pH of the water,especially when the mine waste water is initially acidic, which maycause previously soluble minerals and the like to precipitate. Thus,ozofractionation and subsequent separation of any precipitate that formsmay be sufficient to treat certain types of mine waste water.

In some embodiments, the mine waste water is ozofractionated by causinga foam comprising ozone to pass through the mine waste water. Typically,the mine waste water is caused to flow through a chamber whilst a foamcomprising ozone is caused to rise from a bottom portion of the chamberto a top portion of the chamber.

In some embodiments, the mine waste water is caused to flow through achamber in an opposite direction to a foam comprising ozone that iscaused to rise from the bottom portion of the chamber to the top portionof the chamber.

In some embodiments, the foam of ozone is delivered by venturiinjection.

In some embodiments, at least a portion of a foam fractionate is removedfrom the surface of the ozofractionated mine waste water. Such a foamfractionate may include contaminants removed from the mine waste watersimilar to those discussed above in relation to industrial fluid wastesgenerally.

In some embodiments, the method may comprise a preliminary step in whichparameters of the mine waste water are monitored and used to determineozofractionation conditions.

The duration of ozofractionation will depend on the nature of the minewaste water and can be determined empirically based on the target c.tfor the waste source, as discussed above in relation to industrial fluidwastes generally. For heavily contaminated waste water, ozofractionationtimes may be up to 2 or 3 or even 4 hours. For lightly contaminatedwaste water, ozofractionation times may be as little as 30 seconds. Insome embodiments, the mine waste water is ozofractionated for about onehour.

The quantity of ozone required to ozofractionate the mine waste waterwill also depend on the nature of the mine waste water and can bedetermined empirically based on the target c.t for the waste source, asdiscussed above in relation to industrial fluid wastes generally. Forheavily contaminated waste water, about 4 to about 8 (e.g. about 5, 6, 7or 8 g) grams of ozone for every kilolitre of mine waste water may berequired. For lightly contaminated waste water, about 0.5 to about 3(e.g. about 1, 2 or 3 g) grams of ozone for every kilolitre of minewaste water may be required. In some embodiments, the mine waste wateris ozofractionated using about 4 grams of ozone for every kilolitre ofmine waste water.

In some embodiments, the precipitated metal species are separated fromthe ozofractionated water by allowing the precipitated metal species tosettle and then decanting the supernatant ozofractionated liquid.

In some embodiments, ozofractionation may not be sufficient toadequately treat the mine waste water (e.g. the pH of theozofractionated mine waste water may be not appropriate for dischargeinto the environment, or the ozofractionated mine waste water may stillcontain some dissolved metallic species or other contaminants). Thus,some embodiments may comprise an additional step of monitoringparameters of the ozofractionated water and, if certain conditions aremet, the ozofractionated water is deemed to require further treatmentbefore discharge. Thus, in some embodiments, it may be necessary to adda further treating agent or agents (e.g. a pH adjusting agent and/or abinding agent) to the ozofractionated water. Alternatively (or inaddition), some embodiments may comprise an additional step of exposingthe ozofractionated water to UV light, which can destroy somecontaminant found in the mine waste water.

Mine waste water may be acidic, basic or neutral. For example, thecondition of water quality from underground mines, or backfills ofsurface mines, is dependent on the acid-producing (sulfide) and alkaline(carbonate) minerals in the disturbed rock. In general, sulfide-rich andcarbonate-poor materials produce acidic drainage (e.g. AMD). Incontrast, alkaline-rich materials, even with significant sulfideconcentrations, often produce alkaline conditions in water.

Increasing or decreasing the pH of a solution using a pH adjusting agentis another technique by which species in solution may be caused toprecipitate. For example, in the case of AMD, increasing the pH tobetween about 8.5 to about 9.5 will cause many metallic species toprecipitate and thereby be separable. Thus, changing the pH of theozofractionated water may cause precipitation of additional contaminantsthat may still be present in the water post ozofractionation.

In embodiments where the mine waste water post ozofractionation isacidic and it is desirable to increase the pH, the pH adjusting agentwould be a basic agent. In embodiments where the mine waste water isbasic post ozofractionation and it is desirable to decrease the pH, thepH adjusting agent would be an acidic agent. In embodiments where themine waste water is neutral post ozofractionation, either a basic oracidic agent could be used.

Exemplary basic agents include limestone, CaCO₃, hydrated lime, Ca(OH)₂,un-hydrated (quick) lime, CaO, soda ash, Na₂CO₃, caustic soda, NaOH,magna lime, MgO, hydrated potassium aluminium sulphide, red mud andproducts sold under the brand name ViroMine™ Technology.

Exemplary acidic agents include hydrochloric acid, CO₂ and products soldunder the brand name ViroMine™ Technology.

In some embodiments, the further treating agent is a binding agentcapable of sequestering metal species present in the waste water (e.g.that precipitate when the pH adjusting agent is added). Such bindingagents are advantageous because they can sequester mineral content intoa stable matrix safe for land fill. Without such sequestration, metalspecies in the landfill may still be free to migrate, for example, byleeching out when exposed to rainwater or the like.

In some embodiments, the further treating agent is capable of bothadjusting the pH and binding precipitated metal species. For example,agents capable of sequestering mineral content into a stable matrix safefor land fill and adjusting the pH of a solution to which they are addedare sold by Virotec Global Solutions Pty Ltd under the trade nameViroMine™ Technology. The ViroMine™ Technology products are based on redmud, the by-product of bauxite processing in the Bayer process, and area non-hazardous, non-dangerous environmental remediation technologyderived from alumina refinery residues.

As it is significantly alkaline, most ViroMine™ Technology productsraise pH (the pH of red mud is 10-15). In raising pH, certain elementsare caused to precipitate out of solution. In addition, ViroMine™Technology provides a type of absorptive sponge that sequestersprecipitated metal species in a stable matrix. The resultant settledsludge is therefore stable and safe for disposal to land fill. ViroMine™Technology includes five reagents:

-   -   a) Neutra B—a reagent designed to treat mildly acidic (pH 6-8)        water contaminated with heavy metals, particularly arsenic and        selenium;    -   b) Acid B—a reagent designed to treat acidic (pH 4.5-6) water        contaminated with heavy metals;    -   c) Acid B Extra—a reagent designed to treat highly acidic        (pH<4.5) water contaminated with heavy metals;    -   d) Terra B—a reagent designed to treat sulphidic waste rock and        soil; and    -   e) Alka B—a reagent designed to treat alkaline (pH>7) water        contaminated with heavy metals.

In some embodiments, a basic agent, if added, causes the pH of theozotractionated water to become between about 8.5 and about 9.5. This pHis sufficient to cause precipitation of many metallic species oftenpresent in AMD which may have survived the ozofractionation step.

In some embodiments, the parameters of the ozofractionated water thatare monitored to decide whether a further treating agent is requiredinclude the pH and the oxidation reduction potential (ORP) of theozofractionated water. Such parameters are indicative of the suitabilityof the ozofractionated water for disposal into the environment. Otherparameters that could be monitored include flow volume, total suspendedsolids or turbidity (TSS), total dissolved solids (TDS), conductivity,temperature, dissolved oxygen (DO), as well as the concentrations ofammonium, nitrate and chloride.

In embodiments where the mine waste water being treated is AMD, thebasic agent and/or binding agent is typically added to theozofractionated water if the pH of the ozofractionated water is lessthan about 8.5 and the ORP of the ozofractionated water is greater thanabout 400.

In some embodiments, the method comprises the further step of separatingany metal species that precipitate when the pH adjusting agent is added(as well as any other precipitates that may form at this pH). Forexample, the ozofractionated water may be held in a storage vessel whenthe pH adjusting agent is added. The precipitated metal species may thenbe separated from the treated water by allowing the precipitated metalspecies to settle and subsequently decanting the supernatant neutralisedwater.

Alternatively, the ozofractionated water may be held in a fluidized bedfiltration reaction vessel when the pH adjusting agent (and otheragents, if required) is added. The length of time for which theozofractionated water needs to remain in the fluidized bed filtrationreaction vessel will depend on the nature of the waste being treated,and can be determined empirically. In yet other embodiments, otherreagent contact methods appropriate to achieve the desired outcome maybe used.

In the method for removing dissolved metals (as well as other species,as discussed above), the supernatant ozofractionated water and/or thesupernatant treated water may define a treated water outflow, which isready for disposal into the environment.

In some embodiments, the method comprises the further step of filteringthe treated water outflow in order to remove any precipitate that didnot settle.

The pH of the treated water outflow will depend on control conditionspermitted by a regulatory authority such as the Environmental ProtectionAgency (EPA) in Australia. The regulatory authority may in addition setupper limits of pH control for a particular site. Typically, the pH ofthe treated water outflow is between about 8.5 and about 9.5.

The concentration of dissolved metals in the treated water outflow willvary depending on the species, but will be lower than that required bythe regulatory authority.

The present invention may also be used to remediate legacy sources ofpotentially contaminated materials such as stockpiled mine tailings.Current issues facing the industrial and mining industries not onlyinclude treating new contaminated sources but also remediating legacysources, many of which are simply precipitated heavy sludges that areunstable in form and easily re-dissolved into solution and therefore anexisting environmental threat. Legacy sources include the leechings fromtailing dams and encapsulated rock wastes. Such materials are oftenexposed to the environment where contaminants can leech from whenexposed to water (e.g. rain water or floodwater).

An embodiment of the method of the present invention in which acid minedrainage is treated will be described in detail below with reference tothe flow diagram shown in FIG. 2.

Step A: Source Acid Mine Drainage

As described above, acid mine (or metalliferous) drainage (AMD) formswhen sulfide minerals in rocks are exposed to oxidizing conditions incoal and metal mining, highway construction, and other large-scaleexcavations. A waste stream containing AMD is arranged to flow into thetreatment plant, for example, by pumping or under the action of gravity.

Step B: Screening

Before entering the treatment plant, the AMD stream is first screened toremove rocks and other damaging debris from the AMD stream. Usually thisconsists of a screened containment surrounding the AMD delivery pump, incombination with a 1-2 mm screen post pump.

Step C: Heavy Gravity Separation

Ideally, relatively large particles suspended in the AMD stream (whichhas passed through the screen B) are separated from the stream prior tothe treatment process commencing. This settling can be caused to occurby allowing the AMD to reside in a gravity separation vessel for aperiod of time. Heavy gravity separation may be allowed to occur in asettlement tank, hydrocyclone or even in a sump.

The AMD stream flows from the heavy gravity separation step to the nextstage (ozofractionation) past one or more meters adapted to monitorparameters of the AMD. The parameters monitored are usually flow, pH andtotal suspended solids or turbidity (TSS), but oxidisation reductionpotential (ORP), total dissolved solids (TDS), conductivity,temperature, dissolved oxygen (DO), ammonium, nitrate and chloride couldalso be monitored. The monitored parameters are observed and usuallylogged, and used to determine the treatment conditions in later stagesin the process.

Flow through the system is usually controlled by the length of timerequired for the heavy gravity separation to finish. In the event offlow from this step being ≤50% of the design flow, the recirculationloop from E: Settlement/Decant to D: Ozofractionation can be activatedand thereby continuously reprocess and improve the quality of that waterbefore transferring to G: Process Batch.

Step D: Ozofractionation

As discussed above, ozofractionation combines foam fractionation withozone. In this step, any element that can be oxidized is oxidised,usually resulting in soluble elements becoming insoluble and enablingthem to be either gravity separated, fractionated or mechanicallyfiltered. These oxidised metal species either precipitate from thesolution or get caught in the ozone foam and carried to the top of theAMD in the ozofractionation chamber with the foam fractionate.

Ozone will also oxidise many non-metal species present in industrialwaste fluids such as AMD. These oxidised species will also typicallyeither precipitate from the solution or (more commonly) be carried tothe top of the AMD with the foam fractionate.

During ozofractionation, the AMD stream is monitored for ORP,Conductivity, pH, DO and TSS. pH>6, ORP<350 and conductivity at setpoints relevant to the waste stream will trigger a watch event againstthe same levels in E: Settlement and Decant. Conductivity set pointswill depend on the minerals specific to the AMD waste stream and need tobe defined against the mine conditions. These levels are typical of anon-AMD source, such as ground and storm water or an exposed aquifer.Typically AMD will have a pH<6, ORP>400 and high conductivity.

Flow in the ozofractionator is from the top of the chamber to thebottom. Ozone foam is delivered by venturi injection at the bottom ofthe chamber. The resultant rising bubble column creates counter-currentflow characteristics that enable an extended contact time between theozone foam and the AMD. The required ozone concentration and contacttime (c.t) to oxidise sufficient species will depend on the propertiesof the AMD, but the contact time will usually be between about 30seconds and about 4 hours and the amount of ozone will usually bebetween about 0.5 grams and about 4 grams of ozone per kL AMD treated.

Ozone is typically mixed with air before delivery into the AMD stream.The ozone concentration in the gas bubbles delivered to theozofractionation chamber may be as low as 500 mg per cubic meter of airto as much as 22 grams or more of cubic meter of air applied. Therequired c.t and management of it will depend heavily on the flow rateof the AMD stream (higher flow rates require higher ozone dose ratebecause they necessarily have a lower contact time, whereas lower flowrates can achieve the same c.t with a lower does of ozone and anextended contact time).

The fractionate forms at the top of the ozofractionation chamber andpasses to the fractionate collection cup via the dewatering tower.Fractionate is delivered from the fractionate collection cup to I:Fractionate/settled solids & backwash decant/settlement tank.

From near the base of the ozofractionation chamber, the process fluidflows in a continuous process to the base of the E: Settlement/Decantvessel. Settled sediments are periodically removed from the base of theozofractionation chamber to K: Dewatering stock pile.

Step E: Settlement/Decant

The settlement/decant vessel allows the species that precipitated duringozofractionation to settle. The ozofractionated AMD flows into thebottom of this vessel, where the precipitate can settle at the bottom.Once the water in the vessel reaches a certain height, it can overflowinto the F: Batch balancing vessel, which enhances the efficiency of TSSremoval. In smaller plants, E and F may be combined.

Settled sediments are periodically removed from the base of thesettlement/decant vessel to K: Dewatering stock pile.

Step F: Batch Balancing

The batch balancing vessel accepts the water decanted from thesettlement/decant vessel and operates between high and low water levelsto deliver a batch of water for further processing. If the process waterof a particular batch in the batch balancing vessel has pH>8.5, ORP<400or conductivity at a predetermined level relevant to the waste stream,then the waste stream is deemed to have been sufficiently treated, withno further chemical treatment required, and the batch of process wateris pumped directly to H: Fines Filtration.

In such cases, the AMD treatment process can be run at a faster ratethan is possible if further chemical treatment is required. For example,in the event of ground and storm water or aquifer breach events, theprocess has the flexibility to allow greater flow through the processbecause the ORP or conductivity parameters are low. Generally the higherthe quality of the AMD being treated, the faster the rate it can beprocessed.

However, if the water in the batch vessel has pH<8.5, ORP>400 orconductivity at a predetermined level relevant to the waste stream, thenfurther chemical treatment is required and the water in the batchbalancing vessel is batched to G: process batch.

Settled sediments are periodically removed from the base of the batchbalancing vessel and transferred to K: Dewatering Stock Pile.

Step G: Process Batch

In this vessel, the process water is dosed with a pH adjusting agent,which causes many of the soluble minerals remaining in the process waterto precipitate, and, if necessary, a binding agent which sequestersmetal species. The process batch vessel is batch filled with the waterfrom the batch balancing vessel, dosed with the pH adjusting agent andthe mixture thoroughly mixed for about four hours. The batch is thenallowed to settle for a minimum of 20 hours before it is decanted toFines Filtration.

Typically, the AMD will be acidic, and the pH adjusting agent will be abasic agent.

The pH adjusting agent may also be capable of sequestering mineralcontent into a stable matrix safe for land fill. As discussed above,such reagents are sold by Virotec Global Solutions Pty Ltd under thetrade name ViroMine™ Technology. Alternate reagents that can be used toincrease the pH of the process water or cause flocculation include lime,hydrated lime, hydrated potassium aluminium sulphate (alum). Directaddition of red mud is also possible.

The number of process batch vessels will depend on the volume of AMD tobe treated, with a recommended batch total holding capacity of at least150% of anticipated AMD flow. Settlement is extended in relation toplant inflow to allow for efficient decant process. The longer thesettlement time in the process batch vessels, the longer the finefiltration maintenance interval will be, as less suspended solids arecarried over to H: Fines Filtration.

As noted above, this step could also be conducted in a fluidized bedfiltration reaction vessel, or other reagent contact method appropriateto achieve the desired outcome.

Settled sediments are periodically removed from the base of the ProcessBatch vessel(s) to K: Dewatering stock pile.

Step H: Fines Filtration

Fines filtration removes any remaining suspended solids in the treatedAMD stream. Most methods of fines filtration are acceptable, but willdepend on screening size and desired or permit controlled outcome.Hydrocylone, Sand Filters, Membranes and Reverse Osmosis systems are allacceptable technology.

For example, deep bed rapid sand filtration will reliably filter to 5μm. This can be used if TSS is only required to be <30 mg/L andscreening size studies show the suspended solids to be 95% above the 5μm size. If TSS<10 mg/L, then a combination of deep bed rapid sandfiltration and membrane filtration may be used to achieve better than 1μm. It is feasible to use Reverse Osmosis to filter the treated waterfor an even more stringent control requirement.

Typically, Step H: Fines filtration will be an automated backwashingdeep bed rapid sand filtration system that backwashes on both TSSnon-compliance or increase pressure on the feed to the filter. Backwashis directed to Step I: Fractionate, Settled Solids & BackwashDecant/Settlement, where it is able to settle and decant.

Discharge control parameters are monitored immediately post finesfiltration. If control parameters are met, the waste stream isdischarged to J: Discharge. However, if control parameters not met,discharge is redirected to Batch Balancing for re-treatment.

Typical control parameters will be pH and TSS, but may include DO,conductivity, ORP or other parameters required by the regulatoryrequirements of the site.

Step I: Fractionate, Settled Solids & Backwash Decant/Settlement

This vessel has waste delivered to the base of the vessel, where heavysediments are encouraged to settle. The vessel may include baffles toassist this process or may be very deep. Decant from the top of thisvessel overflows to the discharge of E: settlement/decant, where itcombines with decanted water from that vessel to be batched to treatmentfrom F: hatch balancing.

Settled sediments are periodically removed from the base of this vesseland transferred to K: dewatering stock pile.

Step J: Discharge

Discharge to the environment must be accomplished in an environmentallysensitive manner. It is therefore preferable to discharge high volumesof treated water into a trench system to minimise point source erosion.The discharge can be into a creek, river or lake or into a stormwatersystem. The treated water is suitable for irrigation and may be used towater sports fields or parks.

The discharge line system may also include a small storage vessel foruse in the plant for wash downs, backwash etc.

Step K: Dewatering Stock Pile

All vessels that have settlement are arranged such that settled solidsare periodically removed to the dewatering stock pile. This can beaccomplished with progressive cavity sludge pumps, dewateringcompression belts, screws or other dewatering transfer methods. Thedewatering stock pile is bunded and drained such that fluids capturedfrom this stage are transferred to the delivery line of D:Ozofractionation, for re-treatment. The sediments may require dosingwith a binding agent (e.g. Terra B from VitroMine™ Technology),especially if the process has been accelerated (i.e. the only chemicaltreatment was ozofractionation). When the sediments become dewateredthey can be removed to land fill, stock pile or to mill operations,where they can be further processed if desired (e.g. to retrieveminerals from the settled sediments).

As will be appreciated, the process described above allows stringentcontrol of pH, conductivity, TSS and other parameters in AMD treatmentin a semi-continuous batch process. The process uses intensive controland dosing techniques with the oxidative properties of ozofractionationand, optionally, various neutralising agents including reagents producedfrom the Bauxaul process (red mud). The process is capable ofdistinguishing between heavily degraded AMD, ground and stormwater andaquifer flows and can vary the treatment method as necessary.

It will be understood to persons skilled in the art of the inventionthat many modifications may be made without departing from the spiritand scope of the invention.

It is to be understood that any prior art publication referred to hereindoes not constitute an admission that the publication forms part of thecommon general knowledge in the art.

In the claims which follow and in the preceding description of theinvention, except where the context requires otherwise due to expresslanguage or necessary implication, the word “comprise” or variationssuch as “comprises” or “comprising” is used in an inclusive sense, i.e.to specify the presence of the stated features but not to preclude thepresence or addition of further features in various embodiments of theinvention.

The invention claimed is:
 1. A method for removing contaminants from anindustrial fluid waste, the method comprising: ozofractionating theindustrial fluid waste, in an ozofractionating column, by causing foamcomprising ozone to pass upwards through the industrial fluid waste toproduce a rising foam in an ozofractionated fluid, wherein a size ofbubbles in the foam, delivered into the industrial fluid waste, is lessthan or equal to about 200 μm in diameter, wherein the industrial fluidwaste comprises pesticides or organic pollutants and is not domesticwaste, sewage and food processing wastewater, wherein a volume ofbubbles, delivered into the industrial fluid waste, is less than about13% (v/v), and wherein the ozofractionating, in the ozofractionatingcolumn, is carried out for a duration of greater than one hour, andwherein contaminants are oxidised such that either the contaminantsprecipitate to the bottom of the ozofractionating column or becomeassociated with the rising foam; separating a foam fractionate, which ispart of the foam, from the ozofractionated fluid using a foamconcentrator that comprises a foam chamber having a concave profile tostabilise and build up the foam to form a foam buildup, a tower, throughwhich the foam buildup is pushed up from the pressure of rising bubblesin the rising foam, and a foam outlet, which allows an excess risingfoam to flow out of the foam concentrator; and collecting, in a foamfractionate chamber, the excess rising foam flowing out of the foamoutlet.
 2. The method of claim 1, wherein the industrial fluid waste iscaused to flow through the ozofractionating column whilst a foamcomprising ozone is caused to rise from a bottom portion of theozofractionating column to a top portion of the ozofractionating column.3. The method of claim 1, wherein the industrial fluid waste is causedto flow through the ozofractionating column from a top portion of theozofractionating column to a bottom portion of the ozofractionatingcolumn whilst a foam comprising ozone is caused to rise from the bottomportion of the ozofractionating column to the top portion of theozofractionating column.
 4. The method of claim 1, wherein the foamcomprising ozone is delivered by venturi injection.
 5. The method ofclaim 1, comprising a preliminary step of monitoring parameters of theindustrial fluid waste and using the parameters to determine conditionsof the ozofractionating.
 6. The method of claim 1, wherein theindustrial fluid waste is ozofractionated for about one hour.
 7. Themethod of claim 1, wherein the industrial fluid waste undergoes theozofractionating using about 1 to about 4 grams of ozone for everykilolitre of industrial fluid waste.
 8. The method of claim 1, furthercomprising decanting the supernatant water and removing the precipitatefrom the ozofractionating column.
 9. The method of claim 1, wherein theoxidation reduction potential (ORP) of the industrial fluid waste ismaintained above about 400 mV during the ozofractionating.
 10. Themethod of claim 1, further comprising adding a pH adjusting agent to theozofractionated water.
 11. The method of claim 10, wherein the pHadjusting agent is an acidic agent effective to reduce the pH.
 12. Themethod of claim 1, wherein the organic pollutants are persistent organicpollutants.
 13. The method of claim 1 wherein the foam concentratorcomprises a dewatering tower.
 14. The method of claim 13 wherein thefoam concentrator comprises a fractionate collection cup.
 15. The methodof claim 14 wherein the ozofractionating the industrial fluid wastecomprises foam passing up through the dewatering tower and depositingthat foam in the fractionate collection cup.
 16. The method of claim 15further comprising waiting until after the foam fractionate in thefractionate collection cup has formed a stabilised fractionate andthereafter removing the stabilised fractionate from the fractionatecollection cup.
 17. The method of claim 1 further comprising mixing theozone with air at a ratio of between 500 mg and 22 grams of ozone percubic meter of air applied, to form the bubbles delivered into theindustrial fluid waste.
 18. The method of claim 1 further comprisingexposing the bubbles of ozone to UV light, thereby decreasing aproportion of hydroxyl radicals and increasing a proportion of Hydroxideions.
 19. The method of claim 1 further comprising passing a fluidthrough at least one venturi tube to form the bubbles, and theninjecting the bubbles at the bottom of the ozofractionating column.